In recent years, enlargement of semiconductor wafers has been demanded, and a wire saw is exclusively used for slicing workpieces.
The wire saw is a device that enables a wire (a high tensile steel wire) to travel at high speed, and presses a workpiece (e.g., a silicon ingot) against the wire to be sliced while applying slurry to the wire so that many wafers are simultaneously sliced out (see Patent Document 1).
Here, FIG. 6 is a schematic view showing of an example of a conventional general wire saw.
As shown in FIG. 6, a wire saw 101 is mainly constituted of a wire 102 configured to slice a workpiece, a wire guide 103 around which the wire 102 is wound, a tension giving mechanism 104 configured to give tension to the wire 102, workpiece feeding means 105 configured to feed the workpiece to be sliced, a nozzle 106 configured to supply slurry obtained by dispersing and mixing abrasive grains such as SiC fine powder in a coolant at the time of slicing, and others.
The wire 102 is reeled out from one wire reel bobbin 107, passes through the tension giving mechanism 104 formed of, e.g., a powder clutch (a constant torque motor 109) or a dancer roller (a deadweight) (not shown), and enters the wire guide 103 through a traverser 108. The wire 102 is wound around this wire guide 103 for approximately 300 to 400 turns, and then taken up by the other wire reel bobbin 107′ through the other tension giving mechanism 104′.
Further, the wire guide 103 is a roller provided by press-fitting a polyurethane resin into the periphery of a steel cylinder and forming grooves on a surface thereof at a fixed pitch, and the wound wire 102 can be driven in reciprocating directions at a preset cycle by a driving motor 110.
Furthermore, a nozzle 106 is provided near the wire guide 103 and the wound wire 102 so that the slurry can be supplied to the wire guide 103 and the wire 102 from this nozzle 106 at the time of slicing. Moreover, after the slicing, the slurry is discharged as waste slurry.
Such a wire saw 101 is used, appropriate wire tension is applied to the wire 102 by the tension giving mechanism 104, the wire 102 is allowed to travel in the reciprocating directions by the driving motor 110, and the workpiece is sliced while supplying the slurry, thereby providing a desired sliced wafer.
Additionally, as to the wire 102 used in the wire saw, a length of the wire 102 supplied to slice one workpiece is called a new wire supply amount.
The wire 102 corresponding to a length of several hundred km is wound around the wire reel bobbin 107, and a plurality of workpieces are sliced by using the wire 102 wound around this wire reel bobbin 107.
In case of reducing costs required for the wire included in wafer manufacturing costs, there is a method for increasing the number of workpieces that can be sliced per wire reel bobbin by reducing a necessary new wire supply amount per workpiece.
For example, it is assumed that the new wire supply amount used for slicing one workpiece with the wire reel bobbin having 510 km of the wire wound thereon is 170 km, and three workpieces are sliced. When the new wire supply amount used in each slicing process is reduced to half, i.e., 85 km, the number of the workpieces that can be sliced with the use of the same length of the wire, i.e., one wire reel bobbin can be increased to six.
When the new wire supply amount used for slicing each workpiece is reduced in this manner, since an amount of the wire used for slicing each workpiece is lowered, the number of the workpieces that can be sliced with the use of one wire reel bobbin can be increased, and costs required for the wire can be decreased.